Installing & maintaining a Postgres extension is vastly, vastly simpler than running Elasticsearch and Kafka. Like, how could you even compare these things if you know what you are talking about?

Or maybe you are looking at it from "just swipe your credit card at AWS" perspective, in which case "just use Postgres" articles are for a different audience.

Not really, most popular extensions are available on GCP/AWS (https://docs.cloud.google.com/sql/docs/postgres/extensions) out of the box and there's many things that you can easily run in Postgres without extensions (Queue, KV store).